1. Field of the Invention
The present invention relates to an image forming apparatus and a video receiving and display apparatus for displaying a plurality of images based on a video signal corresponding one image.
2. Description of the Related Art
A technique for displaying an image twice by performing two vertical scans on the image based on an input video signal corresponding to one frame so as to reduce flicker or a so-called double-speed display technique is disclosed in Japanese Patent Laid-Open No. 2004-219884.
An image display technique for emitting a light from a device so that a luminance time width in sub-fields is half a time width of the sub-fields (50% duty ratio) is disclosed in Japanese Patent Application Laid-Open No. H09-083911 (corresponding U.S. Pat. Nos. 6,100,939 and 6,333,766).
An image display technique for putting at least one non-display field between two frames and for approximating a display scheme to an impulse display scheme for securing a relatively long non-display time in frames is disclosed in Japanese Patent Application Laid-Open No. 2002-169515.
A video signal refresh rate of an ordinary television broadcast is 50 Hz or 60 Hz. A screen on which video signals are displayed in this cycle often causes a flicker annoyance. The flicker annoyance is obtrusive particularly in a large-screen image display apparatus. To reduce the flicker, the double speed display method for displaying an image twice based on an original video signal corresponding to one frame, and for thereby converting a display refresh rate in to 100 Hz or 120 Hz is known. However, the following phenomena occur in this double speed display method.
To display a moving image in the image display apparatus, a “retinal afterimage” phenomenon is used. For example, if an object moves on a screen, user's eyes follow the object and an afterimage is formed at a fixed position of retina. If a motion of each eye (an expected position) coincides with a position of the object (a display position) at which the object is actually displayed on the screen, it appears as if the object smoothly moves. If a video signal is displayed at the ordinary refresh rate (50 to 60 Hz), the object display position coincides with the expected position and no problems occur as shown in FIG. 14.
According to the double-speed display method, the same image is displayed twice consecutively. Due to this, as shown in FIG. 15, the object position in the second displayed image (inserted image) is deviated from the expected position. As a result, the object is displayed as if it alternately repeats a moving state and a stationary state and the motion of the object appears artificial.
Further, a video signal at a refresh rate of 60 Hz 3-2 pulldown-converted from an original video signal at a refresh rate of 24 Hz is sometimes input to the image display apparatus. As shown in FIG. 16, in the 3-2 pulldown conversion method, an original video signal (F3) corresponding to one frame is 3-2 pulldown-converted into video signals (F3-1, F3-2, and F3-3) corresponding to three frames. An original video signal (F4) corresponding to one frame is 3-2 pulldown-converted into video signals (F4-1 and F4-2) corresponding to two frames. As can be seen, the 3-2 pulldown-converted video signals corresponding to the frames of the original video signals differ in the number of frames. Similarly to the above, in the video displayed by the 3-2 pulldown-converted video signals, therefore, the display position does not coincide with the expected position on the screen and the motion of the object in the video disadvantageously appears artificial.